(1) Field of the Invention
The invention relates to the provision of propulsion power for underwater vehicles, and is directed more particularly to a hydrogen gas generating apparatus which utilizes seawater to generate the hydrogen gas.
(2) Description of the Prior Art
It is known to provide unmanned underwater vehicles (UUV) which are adapted to be launched from submarine torpedo tubes and recovered through the submarine torpedo tube. After recovery, the UUV may be refueled and/or recharged and launched again. Secondary batteries with an electric motor for propulsion meet these requirements but are notably limited in endurance.
Many missions would be available to UUVs if the endurance of such vehicles were substantially longer. It would also be beneficial if in conjunction with improved endurance, the UUV were adapted to run more quietly.
Fuel cells offer several fold improvements over batteries relative to endurance. Of the fuel cells available, the proton exchange membrane (PEM) has been found the most suitable for the undersea requirements of a UUV. However, the PEM fuel cells require both hydrogen and oxygen fuel sources. Hydrogen and oxygen can be stored onboard the UUV as high-pressure compressed gases, but the resulting endurance is only slightly better than with batteries. Further, high-pressure compressed gases are not welcome onboard a submarine. Hydrogen and oxygen may be stored as cryogenic liquids and result in an improvement in endurance of two to three times better than with batteries. However, cryogenic liquids are not welcome onboard submarines. Compressed or cryogenic oxygen is not currently allowed on submarines, nor is compressed or cryogenic hydrogen. While the situation may, in due course, change with respect to oxygen, it is unlikely that there will be a change relative to hydrogen. Hydrogen may be stored by the hydrogenation of metal hydrides, sometimes referred to as “hydrogen sponges”, that release the hydrogen upon addition of heat. While hydrogen sponges might be accepted onboard submarines, the improvement in endurance over batteries is marginal.
Accordingly, there exists a need for a hydrogen gas generating apparatus which is acceptable onboard submarines, can provide sufficient hydrogen gas to PEM driven propulsion systems to afford endurance greatly improved over batteries, and provides means for facilitating quieter operation of the UUV.